Update documentation for SDL 2.0.7 upgrade.

Docs/Urho3D.dox

@@ -232,7 +232,7 @@ Urho3D uses the following third-party libraries:
 - pugixml 1.7 (http://pugixml.org)
 - rapidjson 1.1.0 (https://github.com/miloyip/rapidjson)
 - Recast/Detour (https://github.com/memononen/recastnavigation)
-- SDL 2.0.5 (https://www.libsdl.org)
+- SDL 2.0.7 (https://www.libsdl.org)
 - SQLite 3.20.1 (https://www.sqlite.org)
 - StanHull (https://codesuppository.blogspot.com/2006/03/john-ratcliffs-code-suppository-blog.html)
 - stb_image 2.12 (https://nothings.org)

README.md

@@ -196,7 +196,7 @@ Urho3D uses the following third-party libraries:
 - pugixml 1.7 (http://pugixml.org)
 - rapidjson 1.1.0 (https://github.com/miloyip/rapidjson)
 - Recast/Detour (https://github.com/memononen/recastnavigation)
-- SDL 2.0.5 (https://www.libsdl.org)
+- SDL 2.0.7 (https://www.libsdl.org)
 - SQLite 3.20.1 (https://www.sqlite.org)
 - StanHull (https://codesuppository.blogspot.com/2006/03/john-ratcliffs-code-suppository-blog.html)
 - stb_image 2.12 (https://nothings.org)